1. Field of the Invention
The invention described herein relates to communications systems, and more particularly relates to transmission and processing of segmented or packetized data.
2. Related Art
Channel bonding is the process of taking multiple independent communications channels between two points and treating them as though they were a single “virtual” channel with more total bandwidth than would otherwise be possible. In addition to greater capacity, this arrangement has additional benefits such as increased overall reliability of a virtual channel. Given that a virtual channel is made of multiple physical channels, there is inherent redundancy that allows for continued operation if one or more physical channels fail.
The concept of channel bonding is illustrated generally in the cable communications system of FIG. 1. In this example, a cable modem termination system (CMTS) 110 is shown in communication with a cable modem (CM) 130. Data passes from CMTS 110, via channels 120a through 120i, to CM 130. During a given session, some or all of channels 120a though 120i can be bonded together, so that segmented data for the session (e.g., packets) can be sent through these channels. A given segment or packet will be sent over one of the channels; the next segment or packet may be sent over the same channel, or over a different channel in this bonding channel set (BCS). The CM 130 must then reassemble the segments or packets in order before delivery to an end user.
One approach for sending data on the bonded channels is for the sending end to transmit entire packets, spreading them out among the channels based on load balancing, rate limiting, or other means for selecting channels. Another approach is to concatenate a series of packets into a byte stream, subdividing the stream into segments for transmission on various channels. In either case, the packets/segments are tagged with a sequence number by the transmitting entity (e.g., the CMTS) so that the receiving entity (e.g., the CM) can reproduce the data stream in the proper packet/segment order. This is known as resequencing, and ensures that data is not delivered out of order to the end user.
Resequencing across multiple bonded channels, however, can be a time-intensive process and may consume considerable memory. Segments or packets may be received out of order. At the receiving end, gaps may appear, where a segment or packet goes missing while one or more later numbered segments are received on any of the several bonded channels. Such later numbered segments must be saved in memory until the missing segment is received. At this point the missing segment can be delivered to the end user, along with any saved segments that sequentially follow the missing segment. Such saved segments must be read from memory and delivered to the user in numerical order.
A high-performance, low-cost device like a cable modem can benefit from an efficient method for queuing packets for resequencing. Ideally, an implementation in a CM or CMTS would be fast and not require large amounts of memory/register resources. What is needed, therefore, is a system and method for efficiently resequencing packets or other data segments at a receiving node, wherein the resequencing process requires minimal memory and operates relatively rapidly.
Further embodiments, features, and advantages of the present invention, as well as the operation of the various embodiments of the present invention, are described below with reference to the accompanying drawings.